Method and apparatus for uniformly planarizing a microelectronic substrate

ABSTRACT

A method and apparatus for planarizing a microelectronic substrate. The apparatus can include a planarizing medium having a relatively hard polishing pad and a planarizing liquid disposed on a generally non-porous planarizing surface of the polishing pad. The planarizing liquid can include a colloidal suspension of colloidal particles having generally smooth external surfaces. The colloidal particles can have a variety of shapes, including a spherical shape, a cylindrical shape, a cubic shape, and a hexagonal shape, among others. The colloidal particles can be formed from a variety of materials, including silicon dioxide, manganese oxide, and cerium oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/748,953, filed Dec. 26, 2000, now issued as U.S. Pat. No. 6,450,863which is a continuation of U.S. patent application Ser. No. 09/244,948,filed Feb. 4, 1999, now issued as U.S. Pat. No. 6,176,763.

TECHNICAL FIELD

The present invention relates to methods and apparatuses for uniformlyplanarizing a microelectronic substrate using a chemical-mechanicalplanarization process.

BACKGROUND OF THE INVENTION

Mechanical and chemical-mechanical planarizing processes (collectively“CMP”) are used in the manufacture of microelectronic devices to form aflat surface on semiconductor wafers, field emission displays, and manyother microelectronic substrates. FIG. 1 schematically illustrates aplanarizing machine 10 with a table or platen 20, a carrier assembly 30above the platen 20, a polishing pad 21 positioned on the platen 20, anda planarizing fluid 23 on the polishing pad 21. The planarizing machine10 may also have an under-pad 25 attached to an upper surface 22 of theplaten 20 for supporting the polishing pad 21. In many planarizingmachines, a platen drive assembly 26 rotates (arrow A) and/orreciprocates (arrow B) the platen 20 to move the polishing pad 21 duringplanarization.

The carrier assembly 30 controls and protects a substrate 80 duringplanarization. The carrier assembly 30 typically has a substrate holder32 with a pad 34 that holds the substrate 80 via suction. A carrierdrive assembly 36 typically translates (arrow C) and/or rotates (arrowD) the substrate holder 32. Alternatively, the substrate holder 32 maybe a weighted, free-floating disk (not shown) that slides over thepolishing pad 21. The combination of the polishing pad 21 and theplanarizing fluid 23 generally defines a plananzing medium 28 thatmechanically and/or chemically-mechanically removes material from thesurface of the substrate 80. The polishing pad 21 may be a conventionalpolishing pad composed of a polymeric material (e.g., polyurethane)without abrasive particles, or it may be an abrasive polishing pad withabrasive particles fixedly bonded to a suspension material. In a typicalapplication, the planarizing fluid 23 may be a CMP slurry with abrasiveparticles and chemicals for use with a conventional non-abrasivepolishing pad. In other applications, the planarizing fluid 23 may be achemical solution without abrasive particles for use with an abrasivepolishing pad.

To planarize the substrate 80 with the planarizing machine 10, thecarrier assembly 30 presses the substrate 80 against a planarizingsurface 24 of the polishing pad 21 in the presence of the planarizingfluid 23. The platen 20 and/or the substrate holder 32 move relative toone another to translate the substrate 80 across the planarizing surface24. As a result, the abrasive particles and/or the chemicals in theplanarizing medium 28 remove material from the surface of the substrate80.

CMP processes must consistently and accurately produce a uniform planarsurface on the substrate to enable precise fabrication of circuits andphoto-patterns. Prior to being planarized, many substrates have large“step heights” that create a highly topographic surface across thesubstrate. Yet, as the density of integrated circuits increases, it isnecessary to have a planar substrate surface at several stages ofsubstrate processing because non-uniform substrate surfacessignificantly increase the difficulty of forming sub-micron features orphoto-patterns to within the tolerance of approximately 0.1 microns.Thus, CMP processes must typically transform a highly topographicalsubstrate surface into a highly uniform, planar substrate surface (e.g.,a “blanket surface”).

In one conventional apparatus for planarizing microelectronicsubstrates, the polishing pad 21 includes a relatively soft polyurethanematerial. For example, the polishing pad 21 can be a model numberIC1000, manufactured by Rodel, Inc. of Newark, Del., and described inU.S. Pat. No. 5,489,233 to Cook et al. The polishing pad 21 can includesurface features to increase the polishing rate, as described in Cook etal. and U.S. Pat. No. 5,177,908 to Tuttle. One drawback with thepolishing pads described above is that they may tend to conform to thesurface of the substrate 80 and may therefore not planarize thesubstrate surface uniformly. One approach to addressing this drawback isto increase the hardness and elastic modulus of the polishing pad. Forexample, model number OXP3000 polyurethane polishing pads, having ahardness and elastic modulus greater than the corresponding hardness andelastic modulus of the IC1000 polishing pad, are available from Rodel,Inc.

In another conventional apparatus for planarizing substrates, theplanarizing liquid 23 used with relatively soft polishing pads caninclude a suspension of abrasive fumed silica aggregates 27, such as areshown in FIG. 2. For example, model number ILD1300 planarizing liquidshaving a suspension of fumed silica aggregates 27 such as those shown inFIG. 2, are available from Rodel, Inc. The fumed silica aggregates 27can be formed by reacting SiCl₄ and/or SiH_(x)Cl_(y) with oxygen in aburning process to form SiO₂ particles. As the SiO₂ particles cool, theycollide and adhere to each other, forming the three-dimensionalaggregates 27 having a fractal configuration and a relatively largesurface area.

One problem with the fumed silica aggregates 27 is that they can scratchor otherwise damage the substrate 80 as a result of their rough,three-dimensional shapes. One approach for addressing this problem hasbeen to form abrasive particles having less surface area and lessroughness than the silica aggregates 27. For example, planarizingliquids having spherical abrasive particles are available from Rodel,Inc. under the trade name Klebosol.

One problem with the planarizing solutions having spherical abrasiveparticles occurs when they are used with relatively soft polishing padsand/or with polishing pads having a porous planarizing surface. Thecombination of relatively soft polishing pads and planarizing liquidswith spherical particles may not uniformly planarize the surfaces ofmicroelectronic substrates because the polishing pads may conform to thesurface of the substrate, as discussed above. The porous polishing padmay not planarize the substrate at an acceptable rate because the poresreduce the surface area of the polishing pad that contacts thesubstrate.

SUMMARY OF THE INVENTION

The present invention is directed toward methods and apparatuses foruniformly removing material from a microelectronic substrate duringplanarization. In one aspect of the invention, the apparatus can includea planarizing medium having a polishing pad with a generally non-porousplanarizing surface and a planarizing liquid. The polishing pad can havea Shore D hardness in the range of approximately 58 to approximately 70and/or can have a modulus of elasticity in the range of approximately5.0×10⁸ pascals to approximately 1.5×10⁹ pascals. The planarizing liquidcan include colloidal particles having a generally smooth externalsurface and being dispersed in the planarizing liquid to form acolloidal suspension.

In one aspect of the invention, the colloidal particles can have agenerally spherical shape. In another aspect of the invention, thecolloidal particles can have other shapes with smooth external surfaces,such as a cylindrical shape, a generally cubic shape, a generallyhexagonal shape, or other closed polyhedrons. The colloidal particlescan be formed from silicon dioxide, manganese oxide and/or cerium oxideand/or can have a surface area that is less than the surface area of afumed silica aggregate of approximately the same overall size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional elevation view of achemical-mechanical planarization machine in accordance with the priorart.

FIG. 2 is an isometric view of fumed silica aggregates in accordancewith the prior art.

FIG. 3 is a partial cross-sectional elevation view of achemical-mechanical planarization machine having a planarizing liquidwith smooth-surfaced particles in accordance with an embodiment of thepresent invention.

FIG. 4A is a detailed isometric view of one of the particles shown inFIG. 3 having a spherical shape in accordance with one embodiment of theinvention.

FIG. 4B is a detailed isometric view of one of the particles shown inFIG. 3 having a cylindrical shape in accordance with another embodimentof the invention.

FIG. 4C is an isometric view of one of the particles shown in FIG. 3having a cubic shape in accordance with still another embodiment of theinvention.

FIG. 4D is an isometric view of one of the particles shown in FIG. 3having an elongated rectangular shape in accordance with yet anotherembodiment of the invention.

FIG. 4E is an isometric view of one of the particles shown in FIG. 3having a hexagonal shape in accordance with yet another embodiment ofthe invention.

FIG. 4F is an isometric view of one of the particles shown in FIG. 3having a triangular cross-sectional shape in accordance with stillanother embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed toward methods and apparatuses forplanarizing a microelectronic substrate. The apparatus can include arelatively hard polishing pad in combination with a planarizing liquidhaving a colloidal suspension of smooth-surfaced particles. Manyspecific details of certain embodiments of the invention are set forthin the following description and in FIGS. 3-4F to provide a thoroughunderstanding of such embodiments. One skilled in the art, however, willunderstand that the present invention may have additional embodimentsand that they may be practiced without several of the details describedin the following description.

FIG. 3 illustrates a CMP machine 110 having a platen 120 and aplanarizing medium 128. In the embodiment shown in FIG. 3, theplanarizing medium 128 includes a polishing pad 121 releasably attachedto the platen 120, and a planarizing liquid 123 disposed on aplanarizing surface 124 of the polishing pad 121. The platen 120 can bemovable by means of a platen drive assembly 126 that can impartrotational motion (indicated by arrow A) and/or translational motion(indicated by arrow B) to the platen 120. As was discussed above, theCMP machine 110 can also include a carrier assembly 130 having asubstrate holder 132 and a resilient pad 134 that together press amicroelectronic substrate 180 against the planarizing surface 124 of thepolishing pad 121. A carrier drive assembly 136 can be coupled to thecarrier assembly 130 to move the carrier assembly axially (indicated byarrow C) and/or rotationally (indicated by arrow D) relative to theplaten 120.

In one embodiment, the polishing pad 121 can be relatively hard and havea relatively high modulus of elasticity. For example, the polishing pad121 can include a polyurethane material and can have a hardness,measured on the Shore D hardness scale, of between 58 and 70. In afurther aspect of this embodiment, the polishing pad 121 can have aShore D hardness of approximately 60. The polishing pad 121 can alsohave a modulus of elasticity of between 5.0×10⁸ pascals (7.3×10⁴ psi)and 1.5×10⁹ pascals (2.2×10⁵ psi). In a further aspect of thisembodiment, the modulus of elasticity can be approximately 1.0×10⁹pascals (1.5×10⁵ psi). In still a further aspect of this embodiment, thepolishing pad 121 can have a generally non-porous planarizing surface124. In one embodiment, the polishing pad 121 can be a model numberOXP3000 polishing pad available from Rodel, Inc. of Newark, Del., formedfrom generally non-porous polyurethane and having a hardness and amodulus of elasticity within the ranges identified above. In otherembodiments, other polishing pads 121 from other sources can includematerials other than polyurethane and can have a hardness and/or amodulus of elasticity outside the ranges identified above, so long asthe polishing pads 121 are sufficiently rigid to uniformly planarize themicroelectronic substrate 180.

The planarizing liquid 123 atop the polishing pad 121 can include aliquid medium 129 having a suspension of colloidal particles 127. Forexample, in one embodiment, the liquid medium 129 can include water andammonia or other alkaline substances and can have a pH of approximately11. In another embodiment, the liquid medium 129 can include acidicsubstances and can have a pH of approximately 2.6.

The colloidal particles 127 can have a variety of sizes, shapes andcompositions. For example, in one embodiment, the colloidal particles127 can be spherical and can have a diameter of between 10 nanometersand 300 nanometers. In one aspect of this embodiment, the colloidalparticles 127 can have a diameter of between approximately 30 nanometersand approximately 70 nanometers. In a further aspect of this embodiment,the colloidal particles 127 can have a diameter of approximately 50nanometers, slightly less than the overall size of the fumed silicaaggregates 27 shown in FIG. 2. In other embodiments, the colloidalparticles 127 can have other sizes, so long as they are small enough toremain suspended in the liquid medium 129. Planarizing liquids havingliquid media 129 and colloidal particles 127 within the rangesidentified above are available from Rodel, Inc. under the trade nameKlebosol.

In one embodiment, the colloidal particles 127 can include silicon-basedmolecules, such as silicon dioxide. In other embodiments, the colloidalparticles 127 can include aluminum oxide, manganese oxide and/or ceriumoxide, so long as the colloidal particles 127 have a relatively smallsurface area, as will be discussed in greater detail below withreference to FIGS. 4A-4F.

FIG. 4A is an enlarged isometric view of one of the colloidal particles127 shown in FIG. 3, having a generally spherical overall shape inaccordance with an embodiment of the invention. As shown in FIG. 4A, thecolloidal particle 127 has a smooth external surface. Accordingly, thesurface area of the colloidal particle 127 shown in FIG. 4A issignificantly less than the surface area of a fused aggregate havingapproximately the same overall dimensions, for example, the fused silicaaggregates 27 shown in FIG. 2.

In other embodiments, the colloidal particle 127 can have other shapesthat similarly have smooth external surfaces with relatively low totalsurface area. The surfaces can be generally flat or convex, as opposedto concave, and/or can be generally free of convolutions. For example,the planarizing liquid 123 shown in FIG. 3 can include generallycylindrical colloidal particles 127 b as shown in FIG. 4B, generallycubic colloidal particles 127 c as shown in FIG. 4C, and/or generallyrectangular colloidal particles 127 d as shown in FIG. 4D. In stillfurther embodiments, the planarizing liquid 123 shown in FIG. 3 caninclude colloidal particles 127 e having a generally hexagonal shape asshown in FIG. 4E, and/or colloidal particles 127 f having a generallytriangular cross-sectional shape as shown in FIG. 4F. In still furtherembodiments, the colloidal particles 127 can have other closedpolyhedral shapes, so long as the colloidal particles have generallysmooth exterior surfaces with a relatively low surface area. The shapesof specific colloidal particles 127 can depend on the materialproperties of the particles, the manufacturing processes used to formthe particles, and other variables. For example, the colloidal particles127 can be formed in-situ by “growing” the colloidal particles 127 insolution. Alternatively, the colloidal particles 127 can be formedex-situ, using a process such as pyrolysis, ablation, vapor phasecondensation, grinding or milling, and can then be added to a liquidsolution. In any case, the overall length or diameter of the particlesshown in FIGS. 4A-4F can be within the ranges discussed above withreference to FIG. 3.

An advantage of the combination of the hard polishing pad 121 and thesmooth-surfaced colloidal particles 127 shown in FIGS. 3-4F is thattogether they can uniformly planarize the microelectronic substrate 180without scratching or otherwise damaging the surface of the substrate180. For example, it has been observed in some cases that planarizingwith the hard polishing pad 121 together with the smooth-surfacedcolloidal particles 127 can produce a surface finish on the substrate180 that is smoother than that obtained by planarizing with a hardpolishing pad in combination with fumed silica aggregates. It isbelieved that this effect may result because the smooth-surfacedcolloidal particles 127 may have a lesser tendency than the silicaaggregates to gel or otherwise form agglomerations.

A further advantage of the combination of the hard polishing pad 121 andthe smooth-surfaced colloidal particles 127 is that they can reduce thepotential for scratching the microelectronic substrate 180 duringplanarization. It is believed that scratches in the microelectronicsubstrate 180 may be caused by the rough surfaces of the fumed silicaaggregates 27 (FIG. 2) and/or by large agglomerations of the aggregates27 that become caught between the microelectronic substrate 180 and thepolishing pad 121 (FIG. 3). The colloidal particles 127 may reduce thelikelihood of damaging the microelectronic substrate 180 becauseindividual colloidal particles 127 have smooth surfaces that tend not toscratch the surface of the microelectronic substrate. Furthermore, thecolloidal particles 127 may be less likely to form agglomerationsbecause they do not have fractal shapes that tend to link together.

Still another advantage is that, by reducing the likelihood for formingscratches on the microelectronic substrate 180, the combination of thehard polishing pad 121 and the smooth-surfaced colloidal particles 127may also reduce the likelihood for forming cracks in the microelectronicsubstrate 180. Such cracks can damage structures of the microelectronicsubstrate 180, and can also create channels through which chemicals,such as those used during CMP processing, can damage structures beneaththe surface of the microelectronic substrate 180.

Yet another advantage of an embodiment having a polishing pad 121 with anon-porous planarizing surface 124 is that the combination of such apolishing pad with the smooth-surfaced colloidal particles can increasethe rate at which the microelectronic substrate 180 is planarized whilereducing the likelihood of scratching or otherwise damaging themicroelectronic substrate 180. Such a combination may be particularlyadvantageous when compared with a porous polishing pad such as an ESMpolishing pad, available from James H. Rhodes and Co. of FranklinSprings, N.Y. Such porous polishing pads have a reduced surface area incontact with the microelectronic substrate 180 and accordingly can havea slower planarization rate.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

What is claimed is:
 1. A method for removing material from a surface ofa microelectronic substrate, comprising: selecting a polishing pad tohave a generally non-porous planarizing surface and at least one of amodulus of elasticity in the range of approximately 5.0×10⁸ pascals toapproximately 1.5×10⁹ pascals and a Shore D hardness in the range ofapproximately 58 to approximately 70; selecting a planarizing liquid toinclude a colloid having colloidal particles with a generally closedpolyhedral shape with a length, the colloidal particles further havingexternal non-concave surfaces with a surface roughness having a meanheight of between at least approximately 0.01% and at leastapproximately 10% of the particle length; disposing the planarizingliquid and the colloidal particles on a planarizing surface of thepolishing pad; engaging the surface of the microelectronic substratewith the planarizing liquid and the planarizing surface of the polishingpad; and moving at least one of the microelectronic substrate and thepolishing pad relative to the other of the microelectronic substrate andthe polishing pad to remove material from the surface of themicroelectronic substrate.
 2. The method of claim 1 wherein engaging thesurface of the microelectronic substrate includes interposing thecolloidal particles between the surface of the microelectronic substrateand a planarizing surface of the polishing pad.
 3. The method of claim 1wherein selecting the polishing pad includes selecting a Shore Dhardness of the polishing pad to be approximately
 60. 4. The method ofclaim 1 wherein selecting the polishing pad includes selecting amaterial comprising the polishing pad to have a modulus of elasticity ofapproximately 1.0×10⁹ pascals.
 5. The method of claim 1 whereinselecting the polishing pad includes selecting a material comprising thepolishing pad to include polyurethane.
 6. The method of claim 1 whereinselecting the planarizing liquid includes selecting a materialcomprising the colloidal particles from aluminum oxide silicon dioxide,manganese oxide and cerium oxide.
 7. The method of claim 1 whereinselecting the planarizing liquid includes selecting a shape of thecolloidal particles from a generally spherical shape, a generallycylindrical shape, a generally cubic shape, and a generally hexagonalshape.
 8. The method of claim 1 wherein selecting the planarizing liquidincludes selecting the colloidal particles to have a length in the rangeof approximately 10 nanometers to approximately 300 nanometers.
 9. Themethod of claim 1 wherein selecting the planarizing liquid includesselecting the colloidal particles to have a length of approximately 50nanometers.
 10. The method of claim 1 wherein selecting the planarizingliquid includes selecting particles of the colloid to have a diameter ofapproximately 50 nanometers.
 11. The method of claim 1 wherein selectingthe planarizing liquid includes selecting the colloidal particles tohave a surface area less than a surface area of a fumed silica aggregatehaving approximately the same overall size.